In multi-carrier or carrier aggregation (CA) operation, a user equipment (UE) is able to receive and/or transmit data to more than one serving cell. In other words, a CA capable UE can be configured to operate with more than one serving cell. The carrier of each serving cell is generally referred to as a component carrier (CC). In general, CC refers to an individual carrier in a multi-carrier system. As used herein, CA may be interchangeably referred to as “multi-carrier system,” “multi-cell operation,” “multi-carrier operation,” “multi-carrier” transmission and/or reception. This means CA may be used for transmission of signaling and data in the uplink (UL) and downlink (DL) directions. One of the CCs is the primary component carrier (PCC) or simply “primary carrier” or even “anchor carrier.” The remaining CCs are referred to as secondary component carrier (SCC) or simply “secondary carriers” or even “supplementary carriers.” The serving cell may be interchangeably referred to as the primary cell (PCell) or primary serving cell (PSC). Similarly, the secondary serving cell may be interchangeably referred to as the secondary cell (SCell) or secondary serving cell (SSC).
Generally, the primary or anchor CC carries the essential UE specific signaling. The primary CC (also known as PCC or PCell) exists in both UL and DL directions in CA. If there is a single UL CC, the PCell is on that CC. The network may assign different primary carriers to different UEs operating in the same sector or cell.
As used herein, multi-carrier SCell setup refers to a procedure that enables a network node to at least temporarily setup or release the use of an SCell in DL and/or UL by the CA capable UE. The SCell setup or release procedure or command can perform any one or more of the following: configuration of SCell(s) (also known as SCell addition); de-configuration of SCell(s) (also known as SCell release); activation of SCell(s); and deactivation of SCell(s)
A configuration procedure (i.e., addition and/or release of SCell(s)) is used by the serving radio network node (e.g., an eNode B (eNB) in Long Term Evolution (LTE) or Node B and/or radio network controller (RNC) in High Speed Packet Access (HSPA)) to configure a CA capable UE with one or more SCells (e.g., DL SCell, UL SCell or both). A de-configuration procedure, on the other hand, is used by the eNB to de-configure or remove one or more already configured SCells (e.g., DL SCell, UL SCell or both). The configuration or de-configuration procedures are also used to change the current multi-carrier configuration (e.g., for increasing or decreasing the number of SCells or for swapping the existing SCell(s) with new one(s)). Configuration and de-configuration is done by the network node (e.g., eNB) and by RNC using Radio Resource Control (RRC) signaling in LTE and HSPA, respectively.
The serving radio network node (e.g., eNB in LTE or Node B in HSPA) can activate one or more deactivated SCells or deactivate one or more SCells on the corresponding configured secondary carriers. The PCell is always activated. The configured SCells are initially deactivated upon addition and after a cell change (e.g., handover). In HSPA, the activation and deactivation command is sent by the Node B via the High-Speed Shared Control Channel (HS-SCCH). In LTE, the activation and deactivation command is sent by the eNB via a Medium Access Control (MAC) control element (MAC-CE). The deactivation of SCell saves UE battery power.
A SCell setup or release (i.e., when SCell is configured, de-configured, activated or deactivated) may cause a glitch or interruption of operation (e.g., reception and/or transmission on signals) on the PCell or any other activated SCell. The glitch or interruption in UL and/or DL typically occurs when the UE has a single radio chain to receive and/or transmit more than one CC. The glitch or interruption, however, may also occur when the UE has independent radio chains on the same chip. The glitch or interruption mainly occurs when the CA capable UE changes its reception and/or transmission bandwidth from single-carrier to multiple-carrier operation (or vice versa). In order to change the bandwidth, the UE has to reconfigure its radio frequency (RF) components in the RF chain (e.g., RF filter, power amplifier (PA), etc.). The glitch or interruption can vary between 2-5 ms. The interruption is due to several factors, including RF tuning to reconfigure bandwidth (e.g., shorten or extend), setting or adjusting of radio parameter(s) (e.g., Automatic Gain Control (AGC) setting), and other factors.
According to existing approaches, an interruption on PCell of up to 5 subframes is allowed for intra-band CA when any of the SCell setup or release procedures are executed by the UE. An interruption on PCell of up to 1 subframe is allowed, however, for inter-band CA when any of the SCell setup or release procedures are executed by the UE. When multiple SCCs are configured, then this requirement extends to the PCell and any activated SCell.
During the interruption period, the UE is unable to perform certain functions. For example, during the interruption period the UE cannot receive from and/or transmit any signal or information to the network. As another example, during the interruption the UE cannot perform measurements due to its inability to receive and/or transmit signals. This leads to the loss or dropping of packets transmitted between the UE and its serving cell(s). The interruption may impact several or all active carriers, and may affect both the UL and DL.
The UE may perform measurements on deactivated SCell(s) or other cells on the SCC with deactivated SCell. In such a case, the measurements are performed in measurement cycles configured by higher layers. The Positioning Reference Signal (PRS) configuration for Reference Signal Time Difference (RSTD) and SCell measurement cycle used for mobility measurements (e.g., Reference Signal Received Power (RSRP) and Reference Signal Received Quality (RSRQ)) are examples of measurement cycles. The SCell measurement cycles may have a periodicity of 160 ms, 320 ms, 640 ms or 1024 ms. The maximum time of a measurement within each measurement cycle is currently not restricted by the standard, but in practice it is likely to be up to 6 subframes in each cycle.
FIG. 1 illustrates interruption on PCC due to measurements on one or more cells of SCC with deactivated SCell. More particularly, FIG. 1 illustrates time 105 on the X-axis, interruptions on PCC 110a, 110b, and measurement sample 115. When performing measurement 115 on cells of the SCC with deactivated SCell(s) without gaps, the UE typically retunes its receiver. The cells may, for example, be SCell and/or one or more neighbor cells of that SCC. Therefore, interruptions 110a and 110b in DL and/or UL of the serving cell occur before and after each measurement sample 115 (i.e., when the bandwidth is extended (e.g., from 20 MHz to 40 MHz)) and also when it is reverted back to the bandwidth of the serving carriers (e.g., from 40 MHz to 20 MHz). Interruptions 110 may also occur when the serving carrier and the SCC are on the same chip. Interruptions 110 in each direction in this case can be between 2-5 ms because the UE has to retune the center frequency and the bandwidth of the DL. The UE does measurements on cells of SCC with deactivated SCell(s) on a regular basis according to the SCell measurement cycle configured by the network node (e.g., eNB).
The current requirement on the maximum allowed interruptions due to measurements on SCC with deactivated SCell is up to 0.5% probability of missed Acknowledgement (ACK)/Negative Acknowledgement (NACK) when the configured measCycleSCell (as described in 3GPP TS 36.331, v.13.0.0) is 640 ms or longer. Furthermore, when multiple SCCs are configured, there is also a requirement that an interruption on any activated SCell should not exceed 0.5% probability of missed ACK/NACK when the configured measCycleSCell for the deactivated SCell is 640 ms or longer.
In LTE, the UE may also perform discovery signal measurements. Examples of measurements that can be performed by the UE on discovery signals include cell search (also known as cell identification), RSRP, RSRQ, Channel State Information (CSI), CSI-RSRP, CSI-RSRQ, Channel Quality Indicators (CQI), UE Receive-Transmit (Rx-Tx) time difference, Signal to Interference plus Noise Ratio (SINR), Discovery Reference Signal-SINR (DRS-SINR), and other measurements. Examples of discovery signals include Primary Synchronization Sequence (PSS), Secondary Synchronization Sequence (SSS), common reference symbols (CRS), channel state information reference symbols (CSI-RS), PRS, and other discovery signals.
The discovery signals can be transmitted in a cell in a discovery occasion with some periodicity (also known as discovery occasion periodicity) as part of a discovery measurement configuration (also known as discovery signal measurement configuration). The discovery occasion may contain a certain number of subframes with discovery signals (e.g., between 1-6 subframes). Examples of discovery occasion periodicity include 40 ms, 80 ms and 160 ms. The DRS occasion may also be referred to as discovery signal occasion, discovery signal transmission occasion, and discovery occasion reference signal occasion. The DRS occasion comprises one or more time resources. Examples of time resources include time slot, subframe, symbol, frame, transmission time interval (TTI), interleaving time, and other time resources.
In some cases, the discovery measurement configuration is signalled to the UE via RRC for enabling the UE to perform measurements on cells of one or more carriers (e.g., PCC, SCC, PSC, inter-frequency carrier, etc.). The information element (IE) MeasDS-Config specifies information applicable for discovery signals measurement. The signalled IE is shown below:
MeasDS-Config information elements-- ASN1STARTMeasDS-Config-r12 ::=CHOICE { release NULL, setup SEQUENCE {dmtc-PeriodOffset-r12CHOICE { ms40-r12 INTEGER(0..39), ms80-r12 INTEGER(0..79), ms160-r12 INTEGER(0..159), ...},ds-OccasionDuration-r12 CHOICE { durationFDD-r12 INTEGER(1..maxDS-Duration-r12), durationTDD-r12 INTEGER(2..maxDS-Duration-r12)
The UE sets up the discovery signals measurement timing configuration (DMTC) in accordance with the received dmtc-PeriodOffset. The first subframe of each DMTC occasion occurs at a System Frame Number (SFN) and subframe of the PCell meeting the following conditions: (1) SFN mod T=FLOOR(dmtc-Offset/10); (2) subframe=dmtc-Offset mod 10; and (3) with T=dmtc-Periodicity/10.
Licensed-Assisted Access (LAA), or operation based on frame structure type 3 (specified in 3GPP TS 36.211, v.13.0.0), was introduced in LTE Release 13. It refers to UE operation on at least one carrier in non-licensed spectrum (such as Band 46 also used for WiFi access). For example, a UE can be configured with CA with PCell in Band 1 (licensed spectrum) and SCell in Band 46 (unlicensed spectrum). A network node (e.g., eNB) operating in the unlicensed band only transmits signals that may be used for UE measurements using so called discovery reference symbols (DRS). Unlike Release 8 common reference symbols (CRS), DRS is not transmitted in every subframe. Instead, DRS is transmitted periodically (e.g., every 160 ms). Moreover, the network node may perform so called listen-before-talk (LBT) procedures to check that no other unlicensed node (such as a WiFi access point) is transmitting before it transmits DRS. This means that from a UE perspective, the network node may be unable to transmit any particular DRS transmission. In certain regions, LBT functionality is required from a regulatory point of view to ensure fair coexistence of different radios and access technologies on the unlicensed band.
Examples of LAA measurements in Release 13 include: CRS-based measurements (e.g., RSRP, RSRQ); CSI-based measurements (e.g., CSI-RSRP); UE Received Signal Strength Indicator (RSSI); channel occupancy; cell detection; CSI; PMI; and CQI.
There are three types of RSSI in E-UTRA: (1) non-reportable RSSI used for RSRQ measurements; (2) reportable UE RSSI used for LAA; and (3) eNB RSSI used for LAA. The UE-reportable RSSI used for LAA is specified in 3GPP TS 36.214, v13.0.0, as shown below:
DefinitionE-UTRA Received Signal Strength Indicator (RSSI), comprises the linearaverage of the total received power (in [W]) observed only in the configuredOFDM symbols and in the measurement bandwidth over N number ofresource blocks, by the UE from all sources, including co-channel servingand non-serving cells, adjacent channel interference, thermal noise etc.Higher layers indicate the measurement duration and which OFDMsymbol(s) should be measured by the UE.The reference point for the RSSI shall be the antenna connector of the UE.If receiver diversity is in use by the UE, the reported value shall not be lowerthan the corresponding RSSI of any of the individual diversity branchesApplicableRRC_CONNECTED intra-frequency,forRRC_CONNECTED inter-frequency
FIG. 2 illustrates an example of UE-reportable RSSI measurement for LAA with the RSSI measurement duration of 70 ms. The UE physical layer shall be capable of performing such RSSI measurements on one or more carriers (if the carrier(s) are indicated by higher layers) and reporting the RSSI measurements to higher layers. The UE physical layer shall provide to higher layers a single RSSI sample for each OFDM symbol within each configured RSSI measurement duration occurring with a configured RSSI measurement timing configuration periodicity. The UE can report RSSI in the range of [−100 dBm, −25 dBm] with 1 dBm resolution, and can also report an indication when RSSI is less than −100 dBm or RSSI is greater than or equal to −25 dBm.
For this RSSI, the L1 (physical layer) averaging duration is pre-defined and it is one OFDM symbol. Further, this RSSI is configured by the following parameters (see also FIG. 2): periodicity of UE-reported RSSI measurement duration (also known as RSSI window periodicity) can have values of 40 ms, 80 ms, 160 ms, 320 ms, and 640 ms; measurement duration of UE-reported RSSI measurement (also known as RSSI window) is 1, 14, 28, 42, 70 (in unit of L1 averaging duration); and, optionally, a configurable subframe offset for inter-frequency measurement. When the subframe offset parameter is configured, the UE measures according to the configured offset. When the subframe offset parameter is not configured, the starting offset is chosen randomly by the UE.
The UE-reportable RSSI measurement is used for the channel occupancy measurement, which is a percentage of (per-symbol) samples when the RSSI was above the configured channelOccupancyThreshold for the associated reportConfig. The channel occupancy measurement is reported by the UE to an eNB via RRC, together with the RSSI:
MeasResultForRSSI-r13 ::=SEQUENCE { rssi-Result-r13RSSI-Range-r13, channelOccupancy-r13 INTEGER (0..100)}
According to 3GPP TS 36.331, v13.0.0:                if the measRSSI-ReportConfig is configured within the corresponding reportConfig for this measId:                    2> set the rssi-Result to the average of sample value(s) provided by lower layers in the reportInterval;            2> set the channelOccupancy to the rounded percentage of sample values which are beyond to the channelOccupancyThreshold within all the sample values in the reportInterval;where:                        
ReportInterval ::= ENUMERATED {ms120, ms240, ms480, ms640,ms1024, ms2048, ms5120,ms10240, min1, min6, min12, min30, min60, spare3, spare2, spare1}
The RSSI-based measurements are performed by the UE on one or more carriers during periodic time resources that are configured by the network via RRC signaling. The corresponding measurement configuration is referred to herein as RSSI measurement configuration or simply RSSI configuration. Therefore, both RSSI and channel occupancy measurements are performed by the UE in resources configured according to the RSSI configuration. The corresponding IE is expressed below:
MeasRSSI-Config-r13 ::= CHOICE { release NULL, setup SEQUENCE {rmtc-Period-r13 ENUMERATED {ms40, ms80, ms160, ms320, ms640},rmtc-SubframeOffset-r13 INTEGER(0..639)OPTIONAL, -- Need ONmeasDuration-r13ENUMERATED {sym1, sym14, sym28, sym42, sym70} }}
FIG. 3 illustrates positioning subframe allocation in time for a single cell. More particularly, the example of FIG. 3 illustrates a period of N subframes 305 that includes 6 consecutive subframes forming one positioning occasion 310. In LTE, the positioning node (also known as E-SMLC, SLP or location server) configures the UE to perform one or more positioning measurements. The positioning measurements are used by the UE or positioning node to determine the UE location. The positioning node communicates with the UE and eNodeB in LTE using LPP and LPPa protocols, respectively.
The Observed Time Difference of Arrival (OTDOA) positioning method makes use of the measured timing of DL signals received from multiple eNBs at the UE. For each (measured) neighbor cell, the UE measures RSTD, which is the relative timing difference between a neighbor cell and the reference cell. The RSTD is measured on cell-specific PRS. The PRS are transmitted in pre-defined positioning subframes grouped by several consecutive subframes (NPRS), (i.e., one positioning occasion 310 as shown in the example of FIG. 3). Positioning occasion(s) 310 occur periodically with a certain periodicity 305 of N subframes (i.e., the time interval between two positioning occasions 310). The standardized periods N 305 are 160 ms, 320 ms, 640 ms, and 1280 ms. The number of consecutive subframes 310 may be 1, 2, 4, or 6.
Yet another example of positioning is Enhanced Cell Identity (E-CID). Examples of corresponding measurements include UE Rx-Tx time difference measurement, base station Rx-Tx time difference measurement, timing advance, and other corresponding measurements. These E-CID measurements are performed on CRS in DL and Sounding Reference Signal (SRS) in UL. The SRS is configured by the network at the UE, and is also known as SRS configuration, periodic SRS configuration, and periodic E-CID SRS configuration. To enable the UE and the base station to perform E-CID measurements, SRS are configured with periodic transmission at the UE.
There may be certain deficiencies associated with the existing approaches described above. For example, the current interruption requirements assume that the measurements on deactivated SCells are performed in measurement cycles. RSSI-based measurements, however, generally cannot be performed in measurement cycles due to, for example, shorter RSSI window periodicity and because the times at which the RSSI measurements are to be performed can be configured by the network, while the timing of measurements in measurement cycles are determined by the UE (for a measurement cycle periodicity configured by the network). Furthermore, the RSSI sample duration is 1 symbol, and the RSSI window can be quite small, for example 1 symbol (i.e., for 1 RSSI sample only). This can result in a lot of interruptions when the UE needs multiple RSSI samples. The problem becomes even more severe when there are multiple SCCs. Moreover, the RSSI measurements may also be impacted by interruptions due to SCC setup and/or release procedure(s) on another carrier, and the RSSI configuration is carrier-specific (not cell-specific), while existing interruption requirements are associated with the serving cell of the carrier.